The art has long sought a compound or compounds which would have fungicidal, algicidal and marine antifoulant activity at relatively low concentration levels and also sufficiently low water solubility at useful levels as to be effective for long periods of time without being leached out by water or rain. The compound 1,3-dithiolo (4,5-b)pyrazin- 2-ylidene-propanedinitrile 4-oxide has such a desirable combination of properties. Hereinafter such compound will be referred to as "Compound".